I have a Tamron Adaptall-2 17mm F3.5 which the distance scale window (a glued piece of plastic) had broken off. I wounder what glue can safely glue it back? I have researched into cyanoacrylates aka superglue. I wounder are they safe for this purpose? It seems that it works by dissolving the material in acetone and when being applied, the acetone evaporates and the material forms a strong material bounding the surfaces together. I am mostly worried about acetone evaporating and settling on lens elements.

It works great! Whether it will work on the plastic used for the tamron lens window will depend on what type of plastic it is precisely, but in general terms acrylic like plastic is exactly what this is for.

It works great! Whether it will work on the plastic used for the tamron lens window will depend on what type of plastic it is precisely, but in general terms acrylic like plastic is exactly what this is for.

This one seems to be similar to my green bottle Tamya plastic cement, which AFAIK is mostly acetone. I actually use the fluid to clean up any excess superglue residue, with a Q-tip.